After deciphering the water quality data table (requiring a glossary of 14 acronyms and terms) it looks like my tap water is pretty clean, except for turbidity (suspended particles) and sodium (from road salt and the treatment process). Two of 60 homes tested had high levels of lead, unfortunately not unusual in a city with old water systems and old residential plumbing. The newsletter even boasted about a testing program for pharmaceuticals and personal care products (the D.C. water from the Potomac River has trace amounts of six of these) but they only found nicotine and acetaminophen in small amounts.

I also discovered that, unlike what I assumed, Cambridge does not share a drinking water source with the large Metropolitan Water Resources Authority system that serves the City of Boston. In this map of the MWRA system, the Cambridge drinking water source is located above the tanks just before the aqueduct splits to serve Boston.

Instead, the water comes from the affluent suburbs of Weston, Waltham, Lincoln, and Lexington, where the city funnels a small watershed into two reservoirs for drinking water. Although most of the land is privately owned, Cambridge owns over 1,200 acres of land including the reservoirs and some surrounding land. The water is piped to Fresh Pond in Cambridge, where the treatment plant is located. Tiny diagrams in the report illustrate the watershed and treatment process.

The majority of the watershed is very low density residential neighborhoods in Weston and Lincoln, which show up as a lush green forest on the satellite imagery. This is no doubt the reason for the water quality, and in an interesting way the low density of some of Boston’s exclusive suburbs serves to ensure the extremely urban City of Cambridge with a clean water supply.

The watershed is not without any potential pollutants, however. On their website, the city has detailed maps of zoning, land use, and protection areas in the watershed. The risk map (detail, below) shows the watershed area contains the busy Route 128/I-95, a number of buried petroleum storage tanks (usually at gas stations), and even a capped landfill (see arrow). The city reservoir at Fresh Pond is very close to Danehy Park, build on top of a closed 50-acre city landfill, but presumably the potential for contamination has been thoroughly explored.

What about the commentary on bureaucracy? Below the water quality data is a small note. “In 2008, we had a Monitoring Violation” the city reports. According to a “laboratory scheduling error” the city failed to test for perchlorate in the 3rd quarter of 2008. When they discovered the omission on October 28, 2008, they tested the water and found none detected. Nevertheless, the city reports, “we cannot be sure of the quality of our drinking water during that time.” That’s going in somebody’s annual review.

I took a trip to the Maryland side of Great Falls for the first time this past weekend. It’s hard to believe you’re just 8 miles from the District.

Regular visitors to D.C.’s Shaw-Howard University Metro Station will be familiar with the water. Year-round, a soft trickling sound can be heard in the damp station, and sometimes the water visibly flows over the southbound rail bed. In the photo to the right, the flow has slowed leaving a series of puddles. Although the station is much newer than most others in the system (it opened in 1991), the cement walls are stained with algae and mineral residue left by water. The picture above shows a valve installed directly into the wall to drain water from behind the cement.

All the water is partly due to the station’s construction. It was built just beneath the road surface through a cut-and-cover technique where a hole is excavated and then a roof constructed to create a tunnel. Although the much deeper stations like Dupont Circle also have water problems, they were constructed by drilling directly into bedrock and thus insulated somewhat from subsurface flow. Shaw’s water might have another cause: it is barely one block from a historical stream noteworthy enough to be one of two named streams on eary versions of the L’Enfant Plan.

Labeled “Reedy Branch,” early maps show the stream flowing east from 7th and S st NW in Shaw to join Tiber Creek, and then flowing south just east of North Capitol Street to the Mall. Another version of the L’Enfant plan drawn by Andrew Ellicott in 1792, and shown below, adds the note to the Reedy Branch that “This branch of the Tiber may be conveyed to the Presidents house,” suggesting it is possible the water in the Shaw Station — just south of the natural riverbed — could indeed be the stream.

H-DC has a good listing of D.C.-specific online mapping resources